AU2009357240A1 - Determining and selecting levels of power reduction for signals to be transmitted from a mobile communications device - Google Patents
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- 238000010295 mobile communication Methods 0.000 title claims abstract description 71
- 230000009467 reduction Effects 0.000 title claims abstract description 33
- 238000000034 method Methods 0.000 claims abstract description 65
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/18—TPC being performed according to specific parameters
- H04W52/26—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service]
- H04W52/262—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service] taking into account adaptive modulation and coding [AMC] scheme
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/52—TPC using AGC [Automatic Gain Control] circuits or amplifiers
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Abstract
Levels of power reduction for signals to be transmitted from a mobile communications device via radio channels in a digital wireless communications system, where each signal is modulated according to one of a number of modulation configurations, are determined. For each modulation configuration a first estimate of a power reduction is calculated (101), and the calculated first estimates are storied (102) in the device. The method comprises the steps of determining (103) a limited set of modulation configurations, said limited set comprising modulation configurations that have been determined likely to be used in practice; calculating (104) for each modulation configuration of the limited set an optimized estimate of a power reduction; and storing (105) the calculated optimized estimates in the device. In this way the power consumption of the device is reduced while keeping a look-up table at a reasonable size.
Description
WO 2011/076258 PCT/EP2009/067771 I Determining and selecting levels of power reduction for signals to be transmitted from a mobile communications device 5 Technical Field The embodiments according to the invention relate to determining and select ing levels of power reduction for signals to be transmitted from a mobile communications device via a number of radio channels in a digital wireless communications system, each of said signals being modulated according to 10 one of a number of modulation configurations. Background In cellular systems, energy consumption in the user equipment (UE) is one of the most important aspects to take into consideration when introducing new 15 features and standards. Energy consumption is determined by many parame ters, which differ between different standards, but the power amplifier (PA) is usually a very significant contributor, especially when the user equipment is operating at high output power. 20 The PA efficiency, i.e. the relation between the transmitted and the con sumed power, can be made high by having the power amplifier operate in a non-linear region. This, however, has the side effect that energy is also emit ted in other frequencies than the intended ones, thus causing interference to systems operating at these frequencies. 25 In order to reduce these unwanted out-of-band emissions, the power ampli fier can be made less non-linear, i.e. more linear, by increasing the PA bias, but this again reduces the PA efficiency, and thus it may drastically deterio rate the UE power consumption. In several standards, it is instead allowed in 30 some situations to reduce the maximum transmitted power from its nominal value. The need for this maximum power reduction (MPR) depends on the used signal waveform, which is determined by e.g. the modulation.
WO 2011/076258 PCT/EP2009/067771 2 In WCDMA systems, cubic metric (CM) is typically used as a measure for how much MPR may be applied for a given waveform. A particular WCDMA uplink signal waveform consists of several components associated with dif ferent physical layer parameters such as spreading codes, spreading factors, 5 power levels, and modulation, which all determine the cubic metric of the sig nal in a non-trIvial way. Cubic metric is a heuristic measure, with some numerical constants chosen so that the allowed MPR in dB can be calculated from the cubic metric for 10 WCDMA uplink signals. The basic principle is that different waveforms should be able to fulfill the dimensioning out-of-band requirement (typically Adjacent Channel Leakage power Ratio - ACLR) using the same PA bias. However, it has been found that the MPR indicated by the calculated cubic metric is often over- or underestimated by a substantial amount, compared to what is really 15 required for a particular waveform and a particular power amplifier. Cubic metric is based on the relative amount of power for third order distor tion. It does, however, not consider the distribution of this power in frequency domain, in particular not the distribution between in-band and adjacent chan 20 nels. WCDMA uplink waveforms with the same cubic metric often have com pletely different distributions and thus the cubic metric-based MPR often fails. WO 20081077540 has introduced modulation profiles as the basis for signifi cantly improved MPR estimation. Modulation profiles address the weak 25 nesses of cubic metric. Rather than only quantifying the total third order dis tortion power, the channel distribution for third and higher order products are calculated for every waveform. Each such set of power levels originating from one waveform is referred to as a modulation profile. The modulation profiles can be mapped to MPR in many ways. In this document a simple linear com 30 bination of the modulation profile numbers given in dB was proven to give a sufficient accuracy. Thus with modulation profiles it is possible to easily and quickly calculate accurate MPR values for all waveforms and for different power amplifier characteristics. This enables the design of user equipment WO 2011/076258 PCT/EP2009/067771 3 that can operate with significantly smaller margins on design parameters and therefore with much higher power efficiency. As mentioned above, the required MPR depends on the parameters for the 5 physical channels in a WCDMA signal. In TS 25.101, "User Equipment (UE) radio transmission and reception (FDD)", 3GPP, Release 8, some or all of the following uplink physical channels are used: " DPCCH, which e.g. carries pilot symbols and power control com 10 mands; " DPDCH, which carries data for the transport channel DCH; * HS-DPCCH, which carries feedback information for an associated DL HS-DSCH transmission; " E-DPDCH, which carries data for the transport channel E-DCH; and 15 0 E-DPCCH, which carries control information for the associated E DPCH channel(s). The number of permissible combinations of parameters for these physical channels is very large, above 300 000 for a 3GPP Rel.8 signal. 20 One problem in the existing WCDMA standard is that the cubic metric calcu lation is difficult to do on the fly. Instead, a natural solution is to calculate the cubic metric offline for all possible channel configurations, and store the cor responding allowed MPR in a look-up table. A drawback is that the look-up 25 table needs to be very large, since the number of allowed configurations is more than 300000 in 3GPP ReL. 8. With the introduction of multi-carrier transmission, the issue becomes even bigger, since the number of combina tions grows even more. Thus, any method that simplifies the MPR calculation would be beneficial. 30 Another problem is that the cubic metric often does not give an accurate measure of the MPR that is actually required to fulfill the out-of-band re- WO 2011/076258 PCT/EP2009/067771 4 quirements. This may result in that the power amplifier bias, and hence the power consumption, must be set unnecessarily high. When cubic metric-based MPR values are used the look-up table is kept rela 5 tively small despite the large number of entries. The reason is that the MPR based on cubic metric is specified as numbers rounded to nearest higher value on a 0.5dB grid. Thus, only three bits per entry will be required to rep resent an MPR from the specified range from 0 to 3.5dB. However, if a more accurate MPR should be used, possibly together with optimal power amplifier 10 biasing, the size of the look-up table will increase dramatically. Therefore, it is an object of embodiments of the invention to provide a method of determining levels of power reduction for signals transmitted from a mobile communications device that reduces the power consumption of the 15 device while keeping the look-up tables at a reasonable size. Summary According to embodiments of the invention the object is achieved in a method of determining levels of power reduction for signals to be transmitted 20 from a mobile communications device via a number of radio channels in a digital wireless communications system, each of said signals being modu lated according to one of a number of modulation configurations, the method comprising the step of calculating, for each modulation configuration, a first estimate of a power reduction to be used for transmission from the mobile 25 communications device of signals modulated according to said modulation configuration; and storing the calculated first estimates in the mobile commu nications device. The method further comprises the steps of determining a limited set of modulation configurations, said limited set comprising modula tion configurations that have been determined likely to be used in practice; 30 calculating for each modulation configuration of the limited set an optimized estimate of a power reduction to be used for transmission of signals modu lated according to said modulation configuration; and storing the calculated optimized estimates in the mobile communications device.
WO 2011/076258 PCT/EP2009/067771 5 By determining a limited set of modulation configurations that are likely to be used in practice and calculating optimized estimates of the power reduction only for the configurations of the limited set, it is ensured that the size of the 5 look-up table can be kept reasonable, because the first estimates calculated according to the standard occupies much less memory space than the opti mized estimates. Although the number of permissible combinations of parameters for all the 10 types of physical channels is very large, above 300000 for a 3GPP Rel.8 sig nal most of them will never - or very rarely - be used in practice. For exam ple, for a signal with a given set of physical channels, the spreading codes and the spreading factors are set in accordance with the code rate and the amount of information that the physical channels are carrying. There is then a 15 limited range of settings among the permissible ones for each physical chan nel that is reasonable to apply. Thus the method optimizes the applied MPR with respect to a limited set of physical channel configurations that are determined likely to be used in prac 20 tice. These optimized settings allow a better performance for the limited set of physical channel configurations. For signals not belonging to this set, one may instead use more conservative values of MPR. The method may further comprise the step of calculating at least one of said 25 first estimate and said optimized estimate from modulation dependent data comprising a term calculated from a third order product of a signal modulated according to said modulation configuration. This will typically be the case for the first estimates, which can then be calculated from the cubic metric ac cording to the standard. Alternatively, the method may comprise the step of 30 calculating at least one of said first estimate and said optimized estimate based on characteristics of the signal and a model of a transmitter of the mo bile communications device.
WO 2011/076258 PCT/EP2009/067771 6 The method may further comprise the step of calculating for each modulation configuration of the limited set an optimized set of transmitter settings for the mobile communications device. The set of transmitter settings may comprise at least one of a bias and a supply voltage for a power amplifier of the mobile 5 communications device. Also the power settings of the transmitter influence the power consumption. With the limited set of modulation configurations there is also a limited range of power settings among the permissible ones for each physical channel that is reasonable to apply. Too low power setting will cause the data/control transmission to fail, and too high power setting will 10 only be a waste of power, resulting in increased user equipment battery drain and increased interference level in the network. When the applied MPR as well as the transmitter settings are optimized for the limited set of physical channel configurations, user equipment energy consumption can be reduced for these configurations. For signals not belonging to this set, one may in 15 stead use more conservative values of the settings, such that the user equip ment energy consumption may be considerably higher for these cases. How ever, since these signals presumably are used very rarely, this behavior will affect the overall user equipment battery drain only marginally. With the lim ited set of configurations, accurate MPR and transmitter settings can be 20 stored efficiently in a small look-up table. In one embodiment the method further comprises the steps of determining the limited set of modulation configurations from knowledge of system set tings for a given network vendor or network operator; and calculating and 25 storing said optimized estimates offline. The physical layer parameters to use, including the power settings, are to a large extent signaled to the user equipment by the network. These parameters are typically vendor specific, and it is also possible for the operators to fine-tune them to optimize them for a given deployment. However, the range of reasonable power settings is 30 rather limited, and much smaller than what is allowed by the standard. In ad dition to the signaled parameters, the user equipment may adjust these pa rameters in certain situations, for example when subject to maximum output power constraints.
WO 2011/076258 PCT/EP2009/067771 7 One way of obtaining these settings is when the method further comprises the steps of operating a specimen communications device at different data rates and different modulation configurations in different networks of said 5 digital wireless communications system; recording measurement results dur ing this operation; and obtaining said knowledge of system settings from the recorded measurement results, In another embodiment the method further comprises the steps of receiving 10 system parameters from a network of said digital wireless communications system during operation of the mobile communications device; determining the limited set of modulation configurations from the received system pa rameters in said mobile communications device; and calculating and storing said optimized estimates in said mobile communications device. 15 The method may further comprise the steps of recording during operation of said mobile communications device information about use of different modu lation configurations; updating, if a current limited set of modulation configu rations does not reflect the actual use of modulation configurations, the lim 20 cited set accordingly; and calculating and storing optimized estimates for modulation configurations of the updated, limited set of modulation configura tions. After the optimizations for the first preferred set have been performed, it is possible to continue updating the preferred set based on new signalling and/or observations of what configurations actually are being used. Thus, the 25 look-up table or a part of the look-up table storing MPR and PA bias parame ters can have a variable content. In one embodiment the step of calculating optimal estimates for modulation configurations of the updated set may comprise the steps of generating in 30 transmitter circuitry of said mobile communications device, in a time period where this circuitry is not used for transmitting other signals, a signal corre sponding to a modulation configuration of the updated, limited set of modula- WO 2011/076258 PCT/EP2009/067771 8 tion configurations; and calculating from the generated signal said optimized estimates for this modulation configuration. In another embodiment the step of calculating optimal estimates for modula 5 tion configurations of the updated set may comprise the steps of requesting, when the limited set of modulation configurations has been updated, opti mized estimates for a new modulation configuration of the set from a server containing a database with optimal estimates for all modulation configura tions previously calculated for said mobile communications device; and re 10 ceiving the requested estimates from said server and storing them in said mobile communications device. In yet another embodiment the step of calculating optimal estimates for modulation configurations of the updated set may comprise the steps of 15 transmitting signals modulated according to one of said modulation configu rations from the mobile communications device; receiving said signals in a measurement receiver and determining from the received signals a spectral emission emitted from the mobile communications device during the trans mission of the signals; and calculating from the determined spectral emission 20 optimized estimates for that modulation configuration. The measurement re ceiver may be external to be used off-line, but it is also possible to incorpo rate the measurement receiver in the mobile communications device and use it on-line. 25 Some embodiments of the invention also relate to a method of selecting in a mobile communications device a level of power reduction for a signal to be transmitted from the mobile communications device via a number of radio channels in a digital wireless communications system, the signal being modulated according to one of a number of modulation configurations, the 30 mobile communications device having stored in a memory thereof: first esti mates of a power reduction to be used for transmission of signals from the mobile communications device, wherein a first estimate has been calculated for each of said modulation configurations; and optimized estimates of a WO 2011/076258 PCT/EP2009/067771 9 power reduction to be used for transmission of signals from the mobile com munications device, wherein an optimized estimate has been calculated for each modulation configuration of a limited set of modulation configurations, said limited set comprising modulation configurations that have been deter 5 mined likely to be used in practice. The method comprises the steps of de termining a modulation configuration to be used for modulation of the signal in a subsequent period of time; determining whether said determined modu lation configuration belongs to the limited set of modulation configurations; using, if the determined modulation configuration belongs to the limited set of 10 modulation configurations, the stored optimized estimate for transmission of the signal; and using otherwise the stored first estimate for transmission of the signaL Embodiments corresponding to those mentioned above for the method of 15 determining levels of power reduction also apply for the method of selecting a level of power reduction. Some embodiments of the invention also relate to a mobile communications device configured to transmit signals via a number of radio channels in a digi 20 tal wireless communications system and to modulate transmitted signals ac cording to one of a number of modulation configurations, the device further being configured to use a level of power reduction for a signal to be transmit ted from a mobile communications device, the device comprising a memory having stored therein first estimates of a power reduction to be used for 25 transmission of signals from the mobile communications device, wherein a first estimate has been calculated for each of said modulation configurations; and optimized estimates of a power reduction to be used for transmission of signals from the mobile communications device, wherein an optimized esti mate has been calculated for each modulation configuration of a limited set 30 of modulation configurations, said limited set comprising modulation configu rations that have been determined likely to be used in practice. The device is further configured to determine a modulation configuration to be used for modulation of the signal in a subsequent period of time; determine whether WO 2011/076258 PCT/EP2009/067771 10 said determined modulation configuration belongs to the limited set of modu lation configurations; use, if the determined modulation configuration belongs to the limited set of modulation configurations, the stored optimized estimate for transmission of the signal; and use otherwise the stored first estimate for 5 transmission of the signal. Embodiments corresponding to those mentioned above for the method of selecting a level of power reduction also apply for the mobile communications device. 10 Brief Description of the Drawings Embodiments of the invention will now be described more fully below with reference to the drawings, in which 15 Figure 1 shows a simple block diagram of a transmitter in a mobile terminal; Figure 2 shows a flowchart illustrating how the first and the optimized esti mates can be calculated and stored; 20 Figure 3 shows a flowchart illustrating a mode of operation for an uplink transmitter configured to select between the first and the optimized esti mates; Figure 4 shows an MPR unit with a memory in which the first estimates as 25 well as the optimized estimates are stored; Figure 5 shows a flowchart illustrating one way of determining the limited set of configurations through knowledge of system settings for a network vendor and/or an operator; 30 Figure 6 shows a flowchart illustrating how the limited set can be constructed after receiving system parameters transmitted by the network.
WO 2011/076258 PCT/EP2009/067771 11 Detailed Description of Embodiments In Figure 1 a simple block diagram of a transmitting chain 1 in a mobile ter minal is shown. The mobile terminal may be adapted for use in e.g. a Code Division Multiple Access (CDMA) system or a Wideband Code Division Multi 5 ple Access (WCDMA) system according to the 3GPP standard and arranged to handle some or all of the following uplink physical channels: * DPCCH, which e.g. carries pilot symbols and power control com mands; 10 * DPDCH, which carries data for the transport channel DCH; * HS-DPCCH, which carries feedback information for an associated DL HS-DSCH transmission; * E-DPDCH, which carries data for the transport channel E-DCH; and * E-DPCCH, which carries control information for the associated E 15 DPCH channel(s). The specification for these physical channels allows more than 300 000 dif ferent configurations of signal modulation to be used by the transmitter of the mobile terminal. 20 Five blocks are shown, radio resource control RRC 2, medium access control MAC 3, physical layer 4, Radio 5 and the Power Amplifier PA 6. In the RRC block 2, channels are configured based on control messages from the net work. In this configuration of channels all possible transport format combina 25 tions are given as well as the configuration of each physical channel. The MAC block 3 is handling the data which are to be transmitted on each of the channels. MAC schedules the amount of data which shall be transmitted on each of the channels. In the physical layer 4 the multiplexing of data on the physical channels is performed, the channels are modulated and combined in 30 the waveform generator 9. The resulting signals are then handled by the ra dio circuit 5 and amplified in the power amplifier 6 for transmission via the antenna(s) 7.
WO 2011/076258 PCT/EP2009/067771 12 As mentioned, the transmitter 1 of the mobile terminal may be required to handle more than 300 000 different configurations of signal modulation, each of which has its own unique properties, e.g. with respect to the peak-to average ratio of the signal. If the root-mean-square (RMS) level of signals is 5 kept constant, signals with different peak-to-average ratio will cause different levels of distortion in a nonlinear circuit, such as the power amplifier 6. Since such distortion affects leakage to adjacent channels, also the Adjacent Channel Leakage power Ratio (ACLR), defined as the ratio of a filtered mean power centered on the assigned channel frequency to a filtered mean power 10 centered on an adjacent channel frequency, will be different for each modula tion configuration. To reduce the consequences of this effect, the output power of the power amplifier 6 may be reduced from the nominal maximum output power to a 15 lower value in dependence of the modulation configuration used with the aim of approximately equalizing the ACLR for all modulation configurations. This power reduction is also referred to as back-off. The 3GPP standard includes a maximum allowed level of the power reduction, i.e. a Maximum Power Re duction (MPR). 20 The power reduction can be determined in the MPR unit 8 based on the input from RRC 2 and MAC 3, and this limits the maximum output power transmit ted from the terminal. The calculated back-off is used in the waveform gen eration 9 when transmitting the signal. The MPR calculations may also be 25 used to control the radio block 5 and the power amplifier 6 as it will be de scribed below. As mentioned above, in WCDMA systems, cubic metric (CM) is typically used as a measure for how much MPR may be applied for a given waveform, A 30 particular WCDMA uplink signal waveform consists of several components associated with different physical layer parameters such as spreading codes, spreading factors, power levels, and modulation, which all determine the cu bic metric of the signal in a non-trivial way.
WO 2011/076258 PCT/EP2009/067771 13 Cubic metric is a heuristic measure, with some numerical constants chosen so that the allowed MPR in dB can be calculated from the cubic metric for WCDMA uplink signals. The basic principle is that different waveforms should 5 be able to fulfill the dimensioning out-of-band requirement (typically Adjacent Channel Leakage power Ratio - ACLR) using the same PA bias. However, it has been found that the MPR indicated by the calculated cubic metric is often over- or underestimated by a substantial amount, compared to what is really required for a particular waveform and a particular power amplifier. 10 Cubic metric is based on the relative amount of power for third order distor tion. It does, however, not consider the distribution of this power in frequency domain, in particular not the distribution between in-band and adjacent chan nels. WCDMA uplink waveforms with the same cubic metric often have com 15 pletely different distributions and thus the cubic metric-based MPR often fails. WO 20081077540 has introduced modulation profiles as the basis for signifi cantly improved MPR estimation. Modulation profiles address the weak nesses of cubic metric. Rather than only quantifying the total third order dis 20 tortion power, the channel distribution for third and higher order products is calculated for every waveform. Each such set of power levels originating from one waveform is referred to as a modulation profile. The modulation profiles can be mapped to MPR in many ways. In this document a simple linear com bination of the modulation profile numbers given in dB was proven to give a 25 sufficient accuracy. Thus with modulation profiles it is possible to easily and quickly calculate accurate MPR values for all waveforms and for different power amplifier characteristics. This enables the design of user equipment that can operate with significantly smaller margins on design parameters and therefore with much higher power efficiency. 30 In the existing WCDMA standard the cubic metric calculation is difficult to do on the fly. Instead, a natural solution is to calculate the cubic metric offline for all possible channel configurations, and store the corresponding allowed WO 2011/076258 PCT/EP2009/067771 14 MPR in a look-up table. A drawback is that the look-up table needs to be very large, since the number of allowed configurations may be more than 300000. With the introduction of multi-carrier transmission, the issue becomes even bigger, since the number of combinations grows even more. 5 Further, the cubic metric often does not give an accurate measure of the MPR that is actually required to fulfill the out-of-band requirements. This may result in that the power amplifier bias, and hence the power consumption, must be set unnecessarily high. 10 Although a large number of entries in the look-up table are needed, when cubic metric-based MPR values are used, the look-up table can still be kept relatively small. The reason is that the CM-based MPR is specified as num bers rounded to nearest higher value on a 0.5dB grid. Thus, only three bits 15 per entry will be required to represent an MPR from the specified range from 0 to 3.5dB. However, if a more accurate MPR should be used, possibly to gether with optimal power amplifier biasing, the size of the look-up table will increase dramatically. 20 As mentioned, the number of permissible combinations of parameters for all the above types of physical channels is very large, above 300000 for a 3GPP Rel. 8 signal. However, most of them will never - or very rarely - be used in practice. For example, for a signal with a given set of physical channels, the spreading codes and the spreading factors are set in accordance with the 25 code rate and the amount of information that the physical channels are carry ing. There is then a limited range of power settings among the permissible ones for each physical channel that is reasonable to apply. Too low power setting will cause the data/control transmission to fail, and too high power setting will only be a waste of power, resulting in increased UE battery drain 30 and increased interference level in the network. In an embodiment of the present invention a method is provided to optimize the applied MPR and possibly also the applied transmitter settings, such as WO 2011/076258 PCT/EP2009/067771 15 PA bias settings with respect to a limited set of physical channel configura tions that are determined likely to be used in practice. These optimized set tings are intended to minimize the energy consumption of the user equip ment. For signals not belonging to this set, one may instead use more con 5 servative values of MPR and/or PA bias settings, such that the energy con sumption of the user equipment may be considerably higher for these cases. However, since these signals presumably are used very rarely, this behavior will affect the overall user equipment battery drain only marginally. With the limited set of configurations, accurate MPR and PA biasing parameters can 10 be stored efficiently in a small look-up table. A flowchart 100 illustrating how the standardized and the optimized MPR es timates can be calculated and stored is shown in Figure 2. First, in step 101, a first estimate of the MPR is calculated for each of the above 300000 modu 15 lation configurations according to the standard, e.g. based on the cubic met ric. It is noted that the term "modulation configuration" could here also be read as "physical channel configuration", i.e. it is more than just a modulation format or a set of constellation points; it includes the whole chain from bits to time signal, including e.g. spreading, pulse-shaping, and how to weight and 20 combine the physical channels. The calculated estimates are then stored in the user equipment in step 102. In step 103 a limited set of modulation con figurations most likely to be used in practice is then determined. There are several ways of determining this set, which will be described in detail below. 25 Having determined the limited set, an optimized estimate of the MPR is then calculated for each configuration of the limited set in step 104. As an exam ple, the optimized estimates can be calculated using modulation profiles as described above. Finally, these optimized estimates are then stored in the user equipment in step 105. Naturally, the first estimates as well as the opti 30 mized estimates may also be calculated first and then stored together in the user equipment in one single storing step. This could be the case when the estimates are calculated during the development phase of a new model of WO 2011/076258 PCT/EP2009/067771 16 user equipment and then subsequently stored in each device during the pro duction phase. In order to reduce the amount of required memory in the device, it is possible 5 to calculate and store only sub-optimal estimates of the MPR in step 102. These values need to be less than or equal to the maximum allowed MPR defined by the regulatory requirements. As a consequence, the PA bias may have to be increased in order not to violate emission requirements such as the ACLR. In an extreme case, the first estimates allow for no MPR at all for 10 any physical channel configuration, and the PA bias could be set sufficiently high to ensure ACLR fulfilment for all signals. Such an approach would in crease the power consumption in the device substantially, if the optimization for the limited set is not done properly in steps 103-105. 15 In addition to the optimized estimate of the MPR calculated for each configu ration of the limited set, an optimized set of transmitter settings may also be calculated for these configurations. These optimized settings may include at least one of the bias and the supply voltage of the power amplifier. 20 The physical layer parameters to use, including the power settings, are to a large extent signaled to the user equipment by the network. These parame ters are typically vendor specific, and it is also possible for the operators to fine-tune them to optimize them for a given deployment. However, the range of reasonable power settings is rather limited, and much smaller than what is 25 allowed by the standard. In addition to the signaled parameters, the user equipment may adjust these parameters in certain situations, for example when subject to maximum output power constraints. Thus the present invention is a method to optimize the applied MPR and the 30 applied PA bias with respect to a limited set of physical channel configura tions - in the following referred to as the preferred set or preferred configura tions - that are likely to be used in practice.
WO 2011/076258 PCT/EP2009/067771 17 The basic mode of operation for an uplink WCDMA transmitter employing some embodiments according to the invention is depicted in the flowchart 200 in Figure 3. Each slot, the signal to transmit is created in step 201 ac cording to the currently chosen configuration with its set of physical layer pa 5 rameters, i.e. beta (gain) factors, spreading factors, spreading codes, and modulation. Then in step 202 it is checked whether this configuration belongs to the preferred set, i.e. whether optimized MPR and PA bias values have been calculated for this configuration. 10 If this configuration belongs to the preferred set - i.e. optimized MPR and PA bias values has been stored in the user equipment for this configuration - the corresponding optimal settings are used in step 203. These optimal values are intended to minimize the energy consumption of the user equipment, while still fulfilling the 3GPP requirements with reasonable margin. 15 For signals not belonging to the preferred set, one may use more conserva tive values of MPR and/or PA bias settings, in step 204, such that the energy consumption of the user equipment will be considerably higher for these cases. However, since these signals presumably are used very rarely, this 20 behavior will affect the overall user equipment battery drain only marginally. If this step has been performed, one of the rarely used configurations has ac tually been used, and therefore this configuration may be marked and stored in step 205 as a candidate for future optimization in the case where the pre ferred set of configurations may be modified in the user equipment. 25 Thus, as shown in Figure 4, the MPR unit 8 comprises a memory 11 in which the first estimates 12 of the MPR and sometimes transmitter settings as well as the optimized estimates 13 of the MPR and transmitter settings are stored. A processor 14 checks whether a current configuration belongs to the pre 30 ferred set or not, and accordingly it selects the corresponding estimate from either the optimized or the first estimates as described above.
WO 2011/076258 PCT/EP2009/067771 18 One way of determining the first preferred set of configurations is through knowledge of system settings for one or more network vendors and/or one or more operators. Optimal MPR values and/or PA bias settings (or other transmitter settings) for the preferred set can then be obtained off-line, poten 5 tially taking detailed knowledge of particular PA characteristics into account. The settings can then be preloaded to the user equipment. A procedure fol lowing this scheme is depicted in the flowchart 300 shown in Figure 5. First, in step 301, a list of preferred configurations is obtained e.g. from a network vendor, and then optimal settings for these configurations are calculated. In 10 step 302 it is checked if all configurations of the set have been optimized. If not, optimized values for the next configuration in the list are calculated in step 303. When optimized settings have been calculated for all configurations of the preferred set the calculated values can be stored or preloaded in the user equipment in step 304. 15 In practice, first-hand information of what system settings different ven dors/operators use may not be available. One way then of obtaining such information would be to have test user equipments operate in various net works at a wide variety of data rates, and record the usage of different con 20 figurations. In other embodiments of the invention, the preferred set does not need to be preloaded to the user equipment. One such procedure is depicted in the flowchart 400 shown in Figure 6. Instead, the preferred set can be con 25 structed after receiving system parameters transmitted by the network, from which the preferred set can be derived, and subsequently the corresponding MPR and PA bias optimization can be performed. In step 401, signaled transmit parameters are received from the network, and based on these pa rameters a list of preferred configurations is then created in step 402. The 30 optimal settings for these configurations can then be calculated. In step 403 it is checked if all configurations of the set have been optimized. If not, opti mized values for the next configuration in the list are calculated in step 404.
WO 2011/076258 PCT/EP2009/067771 19 Furthermore, after the optimizations for the first preferred set have been per formed, it is possible to continue updating the preferred set based on new signaling and/or observations of what configurations actually are being used. Therefore, when optimized settings have been calculated for all configura 5 tions of the preferred set the process enters a wait state in step 405 until new preferred configurations are scheduled for optimization. Thus, the look-up table or a part of the look-up table storing MPR and PA bias parameters can have a variable content. 10 In WCDMA, the system settings that are required to calculate a first preferred set include a number of parameters that are sent through RRC (Radio Re source Control) signaling from the network to the user equipment. This sig naling is done on a slow time-scale, mostly during connection set-up phases. Thus, most of these parameters typically do not change over time during the 15 connection. From the signaled parameters, the user equipment may deduct, directly or through calculations, what physical channel configurations to use depending on the number of information bits to be transmitted. The proce dure for retrieving the used channel configurations is described in 3GPP Technical Specifications, e.g. Sec. 4.8.4.1 of TS 25.212, "Multiplexing and 20 channel coding (FDD)", 3GPP, Sec. 4.2.1 of TS 25.213, "Spreading and modulation (FDD)", 3GPP and Sec 5.1.2.5-5.1.2.5B of TS 25.214, "Physical layer procedures (FDD)", 3GPP. The update procedure can be implemented in several ways. For example, 25 parts of the transmitter chain can be used during times when it is actually not used for transmitting any signal. A signal corresponding to a new preferred configuration can be generated in the digital parts of the transmitter chain, whereupon relevant measures such as the cubic metric or preferably modula tion profiles can be calculated, and optimized MPR and PA bias settings can 30 be determined and stored for this configuration. Note that there are no strict timing requirements associated with these calculations, and they can be car red out anytime when the transmitter chain is idle.
WO 2011/076258 PCT/EP2009/067771 20 Another proposal for the update procedure is to invoke a server that contains a database for all configurations and possibly specific for different models of user equipment or models of parts (power amplifiers, TX chips etc) within the user equipment. The user equipment may access such a service when previ 5 ously unused or seldom used configurations are logged as being used fre quently. The user equipment may also access such a service on a regular basis- In the latter case the user equipment may inquire for general updates if the UE manufacturer has identified a need to alter the parameters. 10 The update procedure can also involve the use of a measurement receiver with the purpose of carefully improving PA biasing further that in turn may change the MPR too. This is motivated by the fact that the characteristics of TX chain parts like the power amplifier will differ from the nominal behavior that must otherwise have to be assumed. Also, aging and environmental pa 15 rameters may influence the characteristics. More specifically, a measurement receiver would be used to quantify spectral emission (e.g. ACLR) during normal operation, record the results associated with the particular configura tion in use, apply an optimization algorithm to tune PA biasing and/or MPR slightly for that same configuration when used the next time. The algorithm 20 should optimize the parameters to reach/maintain a desired level of margin in terms of ACLR while maximizing the power efficiency. The measurement re ceiver may be external to be used off-line, but it is also possible to incorpo rate the measurement receiver in the mobile communications device and use it on-line. 25 Existing user equipment implementations may have PA biasing dependent on output power to ensure that the power amplifier is operated efficiently at all levels. This technique may be combined with embodiments of the present invention. Rather than having a single table of PA bias points as a function of 30 output power a vector of such tables should be available where each pre ferred configuration points to the most suitable table. In this way a low mem ory usage may be maintained. The disadvantage is that the bias points can- WO 2011/076258 PCT/EP2009/067771 21 not be tuned as discussed above based on one configuration as a bias point may be addressed by several configurations. If the ability to tune biasing on a per-configuration basis is still desired each 5 such configuration should have its own bias point vs. output power table. This enables further optimization of each configuration at the expense of in creased memory usage. As an alternative to storing actual bias point values in the table the table may instead contain indices to a common list of prede fined bias point settings. Thus, when a bias point for a specific configuration 10 and output power level should be altered the corresponding index is changed to that bias point that best resembles the desired bias point. In many cases the number of bits required specifying a bias point is large but the common list of available bias points can be limited in size (a small subset 15 of all possible combinations). If this is the case using a table with indices to a common bias point settings list for each preferred configuration will be very efficient with respect to memory allocation. Common for all update and tuning procedures described above is that results 20 produced should be checked for compliance with standard specifications. For example, if an MPR value is calculated for a given configuration it should be checked that it is not any higher than the allowed MPR for that configuration. If that is the case the MPR valued stipulated by the standard should be used. 25 Although embodiments according to the invention primarily have been de scribed with respect to WCDMA signals, it may advantageously be applied to other technologies as well. This includes for example extensions to the cur rent WCDMA standard, such as operation over multiple carriers. 30 The methods described above allow for more power efficient operation of user equipment while it is only required to store detailed MPR and PA biasing values for a limited set of configurations thereby significantly reducing mem ory requirements. They also cater for flexibility with respect to the limited WO 2011/076258 PCT/EP2009/067771 22 amount of configurations that can be supported by introducing update mechanisms that can store parameters for new frequently used configura tions at the cost of scrapping less used configurations. This update mecha nism can also be used for further refinement of parameters that may be user 5 equipment specific. They can be combined with the capability to have PA bias points varying with output power. Although various embodiments of the present invention have been described and shown, the invention is not restricted thereto, but may also be embodied 10 in other ways within the scope of the subject-matter defined in the following claims.
Claims (28)
1. A method of determining levels of power reduction for signals to be trans 5 mitted from a mobile communications device (1) via a number of radio chan nels in a digital wireless communications system, each of said signals being modulated according to one of a number of modulation configurations, the method comprising the step of: 0 calculating (101), for each modulation configuration, a first estimate of 10 a power reduction to be used for transmission from the mobile com munications device of signals modulated according to said modulation configuration; and * storing (102) the calculated first estimates in the mobile communica tions device, 15 c h a r a c t e r i z e d in that the method further comprises the steps of: " determining (103) a limited set of modulation configurations, said lim ited set comprising modulation configurations that have been deter mined likely to be used in practice; 20 0 calculating (104) for each modulation configuration of the limited set an optimized estimate of a power reduction to be used for transmis sion of signals modulated according to said modulation configuration; and * storing (105) the calculated optimized estimates in the mobile commu 25 nications device.
2. A method according to claim 1, c h a r a c t e r i z e d in that the method further comprises the step of calculating at least one of said first estimate and said optimized estimate from modulation dependent data com 30 prising a term calculated from a third order product of a signal modulated ac cording to said modulation configuration. WO 2011/076258 PCT/EP2009/067771 24
3. A method according to claim 1, c h a r a c t e r i z e d in that the method further comprises the step of calculating at least one of said first estimate and said optimized estimate based on characteristics of the signal and a model of a transmitter of the mobile communications device. 5
4. A method according to any one of claims 1 to 3, c h a r a c t e r i z e d in that the method further comprises the step of calculating for each modulation configuration of the limited set an optimized set of transmit ter settings for the mobile communications device. 10
5. A method according to claim 4, c h a r a c t e r i z e d in that the set of transmitter settings comprises at least one of a bias and a supply voltage for a power amplifier of the mobile communications device. 15
6. A method according to any one of claims 1 to 5, c h a r a c t e r i z e d in that the method further comprises the steps of: a determining (301) the limited set of modulation configurations from knowledge of system settings for a given network vendor or network operator; and 20 6 calculating (303) and storing (304) said optimized estimates offline.
7. A method according to claim 6, c h a r a c t e r i z e d in that the method further comprises the steps of * operating a specimen communications device at different data rates 25 and different modulation configurations in different networks of said digital wireless communications system; * recording measurement results during this operation; and * obtaining said knowledge of system settings from the recorded meas urement results. 30
8. A method according to any one of claims 1 to 5, c h a r a c t e r i z e d in that the method further comprises the steps of: WO 2011/076258 PCT/EP2009/067771 25 * receiving (401) system parameters from a network of said digital wire less communications system during operation of the mobile communi cations device; s determining (402) the limited set of modulation configurations from the 5 received system parameters in said mobile communications device; and * calculating (404) and storing said optimized estimates in said mobile communications device. 10
9. A method according to any one of claims 1 to 8, c h a r a c t e r i z e d in that the method further comprises the steps of * recording during operation of said mobile communications device in formation about use of different modulation configurations; * updating, if a current limited set of modulation configurations does not 15 reflect the actual use of modulation configurations, the limited set ac cordingly; and * calculating and storing optimized estimates for modulation configura tions of the updated, limited set of modulation configurations. 20
10. A method according to claim 9, c h a r a c t e r i z e d in that the step of calculating optimal estimates for modulation configurations of the updated set comprises the steps of * generating in transmitter circuitry of said mobile communications de vice, in a time period where this circuitry is not used for transmitting 25 other signals, a signal corresponding to a modulation configuration of the updated, limited set of modulation configurations; and a calculating from the generated signal said optimized estimates for this modulation configuration. 30
11. A method according to claim 9, c h a r a c t e r i z e d in that the step of calculating optimal estimates for modulation configurations of the updated set comprises the steps of WO 2011/076258 PCT/EP2009/067771 26 0 requesting, when the limited set of modulation configurations has been updated, optimized estimates for a new modulation configuration of the set from a server containing a database with optimal estimates for all modulation configurations previously calculated for said mobile 5 communications device; and * receiving the requested estimates from said server and storing them in said mobile communications device.
12. A method according to claim 9, c h a r a c t e r i z e d in that 10 the step of calculating optimal estimates for modulation configurations of the updated set comprises the steps of a transmitting signals modulated according to one of said modulation configurations from the mobile communications device; * receiving said signals in a measurement receiver and determining 15 from the received signals a spectral emission emitted from the mobile communications device during the transmission of the signals; and * calculating from the determined spectral emission optimized estimates for that modulation configuration. 20
13. A method of selecting in a mobile communications device (1) a level of power reduction for a signal to be transmitted from the mobile communica tions device via a number of radio channels in a digital wireless communica tions system, the signal being modulated according to one of a number of modulation configurations, 25 the mobile communications device having stored in a memory (11) thereof: * first estimates (12) of a power reduction to be used for transmission of signals from the mobile communications device, wherein a first esti mate has been calculated for each of said modulation configurations; and 30 0 optimized estimates (13) of a power reduction to be used for transmis sion of signals from the mobile communications device, wherein an optimized estimate has been calculated for each modulation configu ration of a limited set of modulation configurations, said limited set WO 2011/076258 PCT/EP2009/067771 27 comprising modulation configurations that have been determined likely to be used in practice, the method comprising the steps of a determining (201) a modulation configuration to be used for modula 5 tion of the signal in a subsequent period of time; a determining (202) whether said determined modulation configuration belongs to the limited set of modulation configurations; * using (203), if the determined modulation configuration belongs to the limited set of modulation configurations, the stored optimized estimate 10 for transmission of the signal; and * using (204) otherwise the stored first estimate for transmission of the signal.
14. A method according to claim 13, c h a r a c t e r i z e d in 15 that the mobile communications device has further stored in its memory for each modulation configuration of the limited set an optimized set of transmit ter settings for the mobile communications device, and that the method fur ther comprises the step of using, if the determined modulation configuration belongs to the limited set of modulation configurations, the stored optimized 20 transmitter settings for transmission of the signal.
15. A method according to claim 14, c h a r a c t e r i z e d in that the set of transmitter settings comprises at least one of a bias and a supply voltage for a power amplifier of the mobile communications device. 25
16. A method according to any one of claims 13 to 15, c h a r a c t e r i z e d in that the method further comprises the steps of: a receiving (401) system parameters from a network of said digital wire less communications system during operation of the mobile communi 30 cations device; * determining (402) the limited set of modulation configurations from the received system parameters in said mobile communications device; and WO 2011/076258 PCT/EP2009/067771 28 e calculating (404) and storing said optimized estimates in said mobile communications device.
17. A method according to any one of claims 13 to 16, c h a r a c 5 t e r i z e d in that the method further comprises the steps of A recording during operation of said mobile communications device in formation about use of different modulation configurations; * updating, if a current limited set of modulation configurations does not reflect the actual use of modulation configurations, the limited set ac 10 cordingly; and * calculating and storing optimized estimates for modulation configura tions of the updated, limited set of modulation configurations.
18. A method according to claim 17, c h a r a c t e r i z e d in 15 that the step of calculating optimal estimates for modulation configurations of the updated set comprises the steps of a generating in transmitter circuitry of said mobile communications de vice, in a time period where this circuitry is not used for transmitting other signals, a signal corresponding to a modulation configuration of 20 the updated, limited set of modulation configurations; and a calculating from the generated signal said optimized estimates for this modulation configuration.
19. A method according to claim 17, c h a r a c t e r i z e d in 25 that the step of calculating optimal estimates for modulation configurations of the updated set comprises the steps of * requesting, when the limited set of modulation configurations has been updated, optimized estimates for a new modulation configuration of the set from a server containing a database with optimal estimates for 30 all modulation configurations previously calculated for said mobile communications device; and " receiving the requested estimates from said server and storing them in said mobile communications device. WO 2011/076258 PCT/EP2009/067771 29
20. A method according to claim 17, c h a r a c t e r i z e d in that the step of calculating optimal estimates for modulation configurations of the updated set comprises the steps of 5 * transmitting signals modulated according to one of said modulation configurations from the mobile communications device; 6 receiving said signals in a measurement receiver and determining from the received signals a spectral emission emitted from the mobile communications device during the transmission of the signals; and 10 * calculating from the determined spectral emission optimized estimates for that modulation configuration.
21. A mobile communications device (1) configured to transmit signals via a number of radio channels in a digital wireless communications system and to 15 modulate transmitted signals according to one of a number of modulation configurations, the device further being configured to use a level of power reduction for a signal to be transmitted from a mobile communications de vice, the device comprising a memory (11) having stored therein: * first estimates (12) of a power reduction to be used for transmission of 20 signals from the mobile communications device, wherein a first esti mate has been calculated for each of said modulation configurations; and * optimized estimates (13) of a power reduction to be used for transmis sion of signals from the mobile communications device, wherein an 25 optimized estimate has been calculated for each modulation configu ration of a limited set of modulation configurations, said limited set comprising modulation configurations that have been determined likely to be used in practice, the device further being configured to 30 a determine a modulation configuration to be used for modulation of the signal in a subsequent period of time; * determine whether said determined modulation configuration belongs to the limited set of modulation configurations; WO 2011/076258 PCT/EP2009/067771 30 * use, if the determined modulation configuration belongs to the limited set of modulation configurations, the stored optimized estimate for transmission of the signal; and * use otherwise the stored first estimate for transmission of the signal. 5
22. A device according to claim 21, c h a r a c t e r i z e d in that the device has further stored in its memory for each modulation configu ration of the limited set an optimized set of transmitter settings for the mobile communications device, and that the device is further configured to use, if the 10 determined modulation configuration belongs to the limited set of modulation configurations, the stored optimized transmitter settings for transmission of the signal.
23. A device according to claim 22, c h a r a c t e r i z e d in 15 that the set of transmitter settings comprises at least one of a bias and a supply voltage for a power amplifier of the mobile communications device.
24. A device according to any one of claims 21 to 23, c h a r a c t e r i z e d in that the device is further configured to: 20 a receive system parameters from a network of said digital wireless communications system during operation of the mobile communica tions device a determine the limited set of modulation configurations from the re ceived system parameters; and 25 0 calculate and storing said optimized estimates.
25. A device according to any one of claims 21 to 24 c h a r a c t e r i z e d in that the device is further configured to: * record during operation of said mobile communications device infor 30 mation about use of different modulation configurations; * update, if a current limited set of modulation configurations does not reflect the actual use of modulation configurations, the limited set ac cordingly; and WO 2011/076258 PCT/EP2009/067771 31 * calculate and store optimized estimates for modulation configurations of the updated, limited set of modulation configurations.
26. A device according to claim 25, c h a r a c t e r i z e d in 5 that the device is further configured to: 0 generate in transmitter circuitry of the mobile communications device, in a time period where this circuitry is not used for transmitting other signals, a signal corresponding to a modulation configuration of the updated, limited set of modulation configurations; and 10 a calculate from the generated signal said optimized estimates for this modulation configuration.
27. A device according to claim 25, c h a r a c t e r i z e d in that the device is further configured to: 15 * request, when the limited set of modulation configurations has been updated, optimized estimates for a new modulation configuration of the set from a server containing a database with optimal estimates for all modulation configurations previously calculated for the mobile com munications device; and 20 * receive the requested estimates from said server and store them in the mobile communications device.
28. A device according to claim 25, c h a r a c t e r i z e d in that the device is further configured to: 25 * transmit signals modulated according to one of said modulation con figurations; * receive said signals in a measurement receiver and determine from the received signals a spectral emission emitted from the device dur ing the transmission of the signals; and 30 * calculate from the determined spectral emission optimized estimates for that modulation configuration.
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| US8811216B2 (en) * | 2009-12-10 | 2014-08-19 | Nokia Corporation | Apparatus and method for cubic metric computation in dual-carrier and multi-carrier wireless communication system |
| WO2012154325A1 (en) * | 2011-04-01 | 2012-11-15 | Interdigital Patent Holdings, Inc. | Method and apparatus for controlling connectivity to a network |
| US8767626B2 (en) | 2011-10-20 | 2014-07-01 | Telefonaktiebolaget L M Ericsson (Publ) | Power reduction for correlated carriers in a cellular communication system |
| DE102015208134A1 (en) | 2015-01-30 | 2016-08-04 | Te Connectivity Germany Gmbh | Arrangement for an electrical switching device |
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| JP2005318266A (en) * | 2004-04-28 | 2005-11-10 | Mitsubishi Electric Corp | Mobile communication terminal device and transmitting power control method |
| US7729715B2 (en) * | 2005-12-30 | 2010-06-01 | Motorola, Inc. | Method and apparatus for power reduction for E-TFC selection |
| WO2007104341A1 (en) | 2006-03-15 | 2007-09-20 | Freescale Semiconductor, Inc. | Method and apparatus for enhanced data rate adaptation and lower power controlin a wlan semiconductor chip |
| US7826810B2 (en) * | 2006-05-08 | 2010-11-02 | Harris Corporation | Multiband radio with transmitter output power optimization |
| US20080171523A1 (en) | 2006-12-20 | 2008-07-17 | Sony Ericsson Mobile Communications Ab | Power Amplifier Bias Control |
| ES2366666T3 (en) | 2006-12-27 | 2011-10-24 | Telefonaktiebolaget Lm Ericsson (Publ) | DETERMINATION OF A POWER REDUCTION LEVEL FOR A TRANSMITTER. |
| CN101617558A (en) * | 2007-02-21 | 2009-12-30 | 日本电气株式会社 | Communication terminal, TFC system of selection and program |
| US20080305824A1 (en) * | 2007-04-20 | 2008-12-11 | Interdigital Technology Corporation | Apparatus and method for computing maximum power reduction for a umts signal |
| US8687676B2 (en) * | 2007-07-30 | 2014-04-01 | Telefonaktiebolaget L M Ericsson (Publ) | Efficient storing of backoff and crestcomp values |
| EP2198649B1 (en) | 2007-10-09 | 2016-11-09 | Telefonaktiebolaget LM Ericsson (publ) | Methods and arrangements in a telecommunication system |
| CN101394253B (en) * | 2008-10-21 | 2011-04-06 | 西安电子科技大学 | Optimized power allocation method reducing interruption rate in encoded collaboration communication |
| US8462757B2 (en) * | 2008-12-15 | 2013-06-11 | Intel Mobile Communications GmbH | Method for adjusting transmitter output power |
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